This invention relates to the manufacture of a sliver having varying thickness along its length used in the production of slub or jaspe yarns, that is yarns which have irregularly disposed thickened regions of different lengths.
In order to obtain such jaspe yarns, which are used to obtain certain types of fabric (boucle fabric or the like) a preparation treatment is required which must be carried out on the semi-worked material before the spinning proper.
Generally such preparation is carried out during the drawing of the yarn, working on the resulting roving by subdividing the web of carding into strips.
As already known, when a roving passes through a drawing frame formed by at least two pairs of pressure rollers arranged in cascade, the rollers of the second pair rotating at a greater speed than those of the first pair, the roving lengthens and takes on the physical and mechanical characteristics required for the following spinning operation.
If, during the drawing stage the speed of the second pair of rollers is changed the consistency and mechanical characteristics of the treated roving are no longer constant and the resulting dimensional variations give rise in the finished product to the jaspe yarn proper.
In general, the variation of speed of the second pair of drawing rollers is caused by programed devices, prepared beforehand, which determine the length of the individual slubs and their arrangement in the yarn.
It is evident that with this system there have to be set up as many slubbing devices as there are drawing frames through which the rovings to be treated pass.
Furthermore, the dimensional variations obtained in the drawing stage reduce the mechanical characteristics of the yarns obtained which, similarly to other characteristics, results in the yarns being less resistant to breakage than those devoid of slubbing.
The object of the present invention is to avoid the above disadvantages by providing an apparatus using a carding engine which allows a reduction in the number of slubbing devices, allowing the drawing frames to remain unchanged and therefore avoiding the costly modifications required to produce a sliver having varying thickness along its length for the manufacture of jaspe yarn, and which allows treatment in a simple and quick way of the semi-worked material from which jaspe yarns are obtained, in such a way that the yarns obtained have better mechanical characteristics than those obtained by the traditional processes.